The structures and mechanisms of formation of the age and cataractous related fluorescent and yellow moieties in human lens proteins will be investigated at the molecular level. Young human lens protein, calf lens protein and synthetic peptides will be irradiated with near UV light under physiological conditions. The impact of physiological and nonphysiological sensitizers and quenchers will also be examined. These include the kynurenine derivatives contained in the human lens. The resulting photolyzed protein will first be compared to human cataractous lens protein on the basis of overall fluorescence, aggregative properties and mobility on electrophoresis. Both the irradiated protein or peptides and cataractous lens protein will be digested and comparisons between the fluorescent or yellow moieties from in vivo and in vitro sources will then be made on the basis of thin layer chromatography and high pressure liquid chromatography techniques. Components exhibiting similar spectral and retentive characteristics will be isolated and structurally determined using natural product techniques (ultraviolet, infrared, nuclear magnetic resonance and mass spectrometry). By these means the extent to which photochemical reactions are involved in the age related and cataractous molecular changes in human lens protein will be unambiguously determined.